Thomas W. Bettge
John W. Weatherly
Warren M. Washington
David Pollard
Bruce P. Briegleb
Warren G. Strand Jr.
CLIMATE AND GLOBAL DYNAMICS DIVISION
NATIONAL CENTER FOR ATMOSPHERIC RESEARCH
BOULDER, COLORADO
| Section | Page No. |
|---|---|
| 1. Introduction | 1 |
| 2. Interaction with the Flux Coupler | 1 |
| a. Spatial and Temporal Coordination | 1 |
| b. Fluxes Exchanged | 2 |
| 3. Thermodynamics | 4 |
| a. Lateral Ice Growth in Leads | 4 |
| b. Lateral Ice Melt | 5 |
| c. Vertical Energy Balance | 6 |
| d. Snow Cover | 8 |
| e. Surface Temperature | 9 |
| f. Penetrating Solar Radiation and Brine Pockets | 10 |
| g. Freshwater Flux | 11 |
| h. Surface Albedo | 11 |
| 4. Dynamics | 13 |
| a. Ice Velocity | 13 |
| b. Advection | 15 |
| 5. Overview of the Sea Ice Model Code | 18 |
| Appendix A -- List of Physical Constants and Parameters | 21 |
| References | 23 |
| Acknowledgments | 25 |
The purpose of this report is to document the details of the governing equations and physical parameterizations of the sea ice model component in the first version of the NCAR Climate System Model (CSM). It should be noted that this model is very similar to the sea ice component used by Washington and Meehl (1996a, 1996b) in a fully coupled model of the atmosphere, ocean, and sea ice. Many of the thermodynamic ice growth and melt processes are taken from previous work, namely Semtner (1976), Parkinson and Washington (1979), Harvey (1988), and Pollard and Thompson (1994). Ice dynamics are based upon the cavitating fluid solution described by Flato and Hibler (1990, 1992), and used by Pollard and Thompson (1994), where the shear and tensile strength of the ice are neglected and the compressive strength is used to iterate to a representative ice velocity each timestep.
The sea ice component of the CSM is driven by the heat, momentum, and freshwater fluxes provided at the upper and lower ice boundaries by the atmospheric and oceanic model components, respectively. In return, the sea ice model provides the appropriate boundary fluxes required by the atmosphere and ocean in the presence of ice. The CSM Flux Coupler (Bryan et al., 1996) facilitates and manages the exchange of fluxes between the CSM component models and exercises the required care to assure conservation of heat, momentum, and freshwater within the model climate system.
We thank the individuals in the Climate and Global Dynamics Division at NCAR who have contributed to the Sea Ice Model used in the Climate System Model, in particular, to Julianna Chow for adapting the model to the ocean model horizontal grid structure; Claire Parkinson (NASA Goddard Space Flight Center, Greenbelt, Maryland) and Gregory Flato (Institute of Ocean Studies, Sidney, British Columbia) for their suggestions; Peter Rayner for his work on an early version of the ice dynamics; Lydia Harper for putting together the final manuscript; and Suzanne Whitman for assistance with the figures.
We acknowledge and appreciate the long-term support of the National Science Foundation (NSF) and the Office of Health and Environmental Research of the U.S. Department of Energy (DOE) as part of the Carbon Dioxide Research Program. Support was also provided by the U.S. Environmental Protection Agency.
The computational resources used in constructing, testing, and applying this model component have been provided by the NSF-supported NCAR Scientific Computing Division, the DOE/National Energy Research Supercomputing Center, the Electric Power Research Institute/University Corporation for Atmospheric Research-sponsored Model Evaluation Consortium for Climate Assessment, and the Arctic Region Supercomputing Center, University of Alaska, Fairbanks.
Figure 3.1 Diagram for the three-layer Semtner (1976) sea ice model. The snow depth, ice thickness, and ice/snow temperatures are calculated on the basis of fluxes across the external and internal boundaries. The energy of penetrating solar radiation is stored in brine pockets and released during freezing. In the CSM Sea Ice Model, all of the energy available to grow ice is used in the lateral growth process, and the heat flux at the bottom of the ice, FB, is assumed to be zero.
Figure 5.1 Conceptual flowchart of the CSM Sea Ice Model code.
